The invention relates to the growth of crystals of Group III metal nitrides. More particularly, the invention relates to the growth of Group III metal nitride crystals by recrystallization from a flux. Even more particularly, the invention relates to the growth of Group III metal nitride crystals by recrystallization from either a solvent or a melt under high pressure, high temperature conditions.
During the past decade there has been considerable interest in the nitrides of the Group III metals (also referred to hereinafter as “Group III metal nitrides”); namely aluminum nitride (also referred to hereinafter as “AlN”), gallium nitride (also referred to hereinafter as “GaN”), and indium nitride (also referred to hereinafter as “InN”) based optoelectronic devices, including, for example, light emitting diodes (LEDs) and laser diodes (LDs). The active layers in such devices typically comprise solid solutions of GaN, AlN, and InN and typically include n-doped layers, p-doped layers, heterostructures, and the like. The performance of these devices, including light emission efficiency, lifetime, and reverse bias current, is often degraded by the presence of threading dislocations, vacancies, and impurities in the active layers and in underlying and overlaying epitaxial layers. Such devices are typically grown on lattice-mismatched substrates such as sapphire or SiC, resulting in a high concentration of threading dislocations that propagate into the active layer. In the case of GaN-based devices, for example, the use of a high quality GaN substrate would greatly reduce the concentration of threading dislocations and other defects in the homoepitaxial active layers and improve device performance.
Gallium nitride single crystals that are of suitable quality for electronic applications have been obtained by reacting nitrogen (N2) gas with gallium metal at pressures and temperatures in the range of 10–20 kilobar and 1200° C. to 1500° C., respectively. Other methods that have been used to grow crystalline GaN include chemical vapor deposition (CVD), hydride vapor phase epitaxy, crystallization in gallium/sodium alloys, and recrystallization from supercritical ammonia. The GaN crystals grown under these conditions exhibit varying degrees of quality and are limited in size. In addition, the growth rate of GaN crystals obtained by these processes is generally low (about 0.1 mm/hr).
The methods that are currently used to grow gallium nitride crystals are unable to produce large crystals of Group III metal nitrides at acceptable growth rates and that are of high quality. Therefore, what is needed is a method of growing Group III metal nitride crystals that are sufficiently large to serve as commercially viable substrates for electronic devices. What is also needed is a method of growing Group III metal nitride crystals that are of high quality and have low concentrations of impurities and dislocations. What is further needed is a method of growing Group III metal nitride crystals at a high growth rate.